The invention relates to an improved apparatus for producing an output signal indicating the thickness or density of sliver strands produced by textile machines such as cards and the like.
One step in the processing of textile fibers such as cotton, wool, synthetic fibers, or any other type of textile fibers is forming these small fibers into a long interlocked chain known in the art as a sliver. This function is usually accomplished by a machine termed a card, but other textile processing equipment such as draw frames and pin drafters also produce slivers. These slivers are conventionally coiled or otherwise stored for further processing into textile yarn or thread which can be then woven or otherwise manipulated into textile material.
It is important that the density or thickness of the sliver be maintained substantially uniform. In the absence of monitoring of this thickness or density, the sliver density has a tendency to drift away from a desired value, thus producing a product which is unsatisfactory for further processing. In view of the speed of operation of modern carding machines, it is virtually impossible for visual observation or periodic manual testing to satisfactorily maintain a desired density.
Thickness regulating devices, commonly known by the term "auto-levelers", are well known in the textile art and have been successfully employed for many years. For example, an auto-leveler manufactured by Crosrol includes a first roller having a groove in the outer peripheral surface thereof in which a second roller rides. Strands produced by a carding machine, after being formed into a sliver, continuingly pass between the two rollers so that the movements of the roller riding in the groove vary as a function of the thickness and density of the sliver. These movements are detected to produce an electrical signal which is integrated and compared electrically with a desired value to control the relative speeds of the doffer and feed rolls of the card machine which in turn controls the sliver density.
British Pat. No. 930,873 describes another textile processing system of this type in which the sliver moves between two rollers with the movement of a second roller on top of the sliver being detected to vary the relative speeds of doffer and feed rolls. In this British patent, a magnet core is mechanically connected to the upper roller and disposed between a primary transformer winding and a pair of secondary windings so that the relative position of the core determines the voltages which appear at the two secondary windings. These secondary windings are in turn used to control a variable speed device which is applied to the feed element of the card machine.
U.S. Pat. No. 3,938,223 describes an apparatus in which the thickness and density of a sliver continuously passing between a rotating grooved roller and a sensor roller riding on the sliver is detected by movement of a magnet core coupled for movement with the upper roller and which is disposed for alternating the coupling between primary and secondary coils of a transformer. Preferably, the transformer includes first and second secondary coils so that the amplitudes of the respective output voltages of these coils are directly related to the position of the core and accordingly, the thickness of the sliver. The signals produced by the two secondary coils are delayed in time by a simple integration circuit to avoid changes in density resulting from detecting a minor irregularity in the sliver and applied to a first differential amplifier which produces an output voltage which varies as a function of the difference between the two input signals.
The output voltage is in turn applied to a second differential amplifier which is periodically rendered operative by a pulse generator for a short period. The other input to the second amplifier is used to adjust the desired sliver thickness. When the second amplifier is activated, an amplified signal is applied to a pair of relays, one responsive to positive excursions of the waveform and the other responsive to negative excursions. Each of these relays operates a controlled switch which, when the relays are activated, completes a current path through a coil of a conventional control device which operates an armature to control a variable speed device connected to one of the two rollers which control the thickness of the sliver, for example, the feed roll on a conventional card.
Auto-levelers have also detected the thickness of a sliver by impinging an air stream onto the sliver as it passes through a trumpet. U.S. Pat. No. 3,710,421 shows one such system in which the back pressure produced by impingement is detected by a pair of interconnected bellows. One of the difficulties with such dual bellow systems is an hysteresis effect in which different pressures are required for movement in opposite directions.
The present invention is a simple and unique apparatus with a trumpet member having a bore extending therethrough through which the sliver passes and a port opening into that bore. The port is connected to a pressure source via an inner bottom averaging compartment of a sensor and a fine metering valve with an air escape port at its outlet. The sensor housing defines an interior space divided by a flexible diaphragm into the lower averaging compartment and an upper compartment at atmospheric pressure. A shaft is fixed to the diaphragm for movement therewith in the lower compartment. A heavy weight which normally rests on the housing floor is fixed to the diaphragm and shaft and in the upper compartment the shaft has a magnetic portion which interacts with a coil wound about the shaft in the upper compartment to produce a signal indicating a change in back pressure in the lower compartment and hence a change in sliver thickness.
The lower averaging compartment thus minimizes oscillation due to fluctuations in thickness or air pressure. Further, the weight defines a substantially constant force which does not require either calibration or recalibration.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.